Conductivity improving additive for fuel oil compositions

ABSTRACT

An fuel oil containing a conductivity improving additive comprising the combination of: (a) an oil soluble succinimide dispersant comprising a functionalized hydrocarbon reacted with an alkylene polyamine and (b) a conductivity improver comprising (i) an olefin polysulfone and (ii) a polymeric polyamine reaction product of epichlorohydrin and an aliphatic primary monoamine or an N-aliphatic hydrocarbyl alkylene diamine, or the sulfonic acid salt of the polymeric polyamine reaction product or (c) the combination of an oil soluble succinimide dispersant comprising a functionalized hydrocarbon reacted with a heavy polyamine and (d) a conductivity improver comprising a hydrocarbon soluble copolymer of an alkylvinyl monomer and a cationic vinyl monomer, wherein the copolymer has an alkylvinyl monomer unit to cationic vinyl monomer unit ratio of from about 1:1 to about 10:1, the copolymer having an average molecular weight of from about 800 to about 1,000,000.

This invention relates to fuel oils which exhibit improved conductivityproperties, to novel additive systems for providing such properties andto the use of such additives for improving the conductivity of fueloils.

U.S. Pat. No. 6,391,070, issued May 21, 2002 to Schield discloses acomposition having increased electrical conductivity, which includes a)a liquid hydrocarbon; b) an anti-static amount of at least onehydrocarbon soluble copolymer of an alkylvinyl monomer and a cationicvinyl monomer, wherein the copolymer has an alkylvinyl monomer unit tocationic vinyl monomer unit ratio of from about 1:1 to about 10:1, thecopolymer having an average molecular weight of from about 800 to about1,000,000; and c) an anti-static amount of at least one hydrocarbonsoluble polysulfone copolymer of at least one olefin and sulfur dioxide.These polymers are described by Schield in U.S. Pat. No. 5,672,183 ascontaining a cationic quaternary ammonium monomer.

U.S. Pat. No. 5,792,730 discloses the use of dispersants prepared fromheavy polyamines as additives for lubricants and fuels.

The present invention is based upon the discovery that the use incombination of an oil soluble succinimide dispersant comprising afunctionalized hydrocarbon reacted with an alkylene polyamine or with aheavy alkylene polyamine with certain commercial conductivity improversresults in a synergistic effect upon the conductivity properties of afuel oil having little or no inherent conductivity.

The invention is particularly useful for the formulation of turbinecombustion fuel oils which are generally those hydrocarbon fuels havingboiling ranges within the limits of about 150° to 600° F. (65 to 315°C.) and are designated by such terms as JP-4, JP-5, JP-7, JP-8, Jet A,Jet A-1. JP-4 and JP-5 are fuels defined by U.S. military specificationMIL-T-5624-N and JP-8 is defined by U.S. Military SpecificationMIL-T83133-D. Jet A, Jet A-1 and Jet B are defined by ASTM specificationD1655.

In accordance with the present invention there has been discovered animproved fuel oil composition comprising a fuel oil having an inherentconductivity of less than 15 pS/m containing an effective conductivityimproving amount of a two component additive system; wherein the twocomponent additive system comprises the combination of:

-   -   (a) an oil soluble succinimide dispersant additive prepared from        a functionalized hydrocarbon or polymer reacted (e.g.        derivatized) with an alkylene polyamine which may be represented        by the formula: HRN (alkylene-NR)nH wherein n has an average        value between 1 and about 11, and in one embodiment about 2 to        about 7, the “alkylene” group has from 1 to about 10 carbon        atoms, and in one embodiment about 2 to about 6 carbon atoms,        and each R is independently hydrogen, an aliphatic or        hydroxy-substituted aliphatic group of up to about 30 carbon        atoms. Some examples of alkylene polyamines include methylene        polyamines, ethylene polyamines, butylene polyamines, propylene        polyamines, pentylene polyamines, etc. Specific examples of such        polyamines include ethylene diamine, diethylene triamine,        triethylene tetramine, propylene diamine, trimethylene diamine,        tripropylene tetramine, tetraethylene pentamine, hexaethylene        heptamine, pentaethylene hexamine, or a mixture of two or more        thereof. Ethylene polyamines such as tetraethylene pentamine and        pentaethylene hexamine are preferred. Suitable alkylene        polyamines also include those termed “heavy polyamines” as        defined hereinbelow; and,    -   (b) a conductivity improver comprising (i) an olefin polysulfone        and (ii) a polymeric polyamine reaction product of        epichlorohydrin and an aliphatic primary monoamine or an        N-aliphatic hydrocarbyl alkylene diamine, or the sulfonic acid        salt of the polymeric polyamine reaction product. The weight        ratio of the olefin polysulfone to the polymeric polyamine will        be in the range of 40:1 to 1:40,    -   or the combination of:    -   (c) an oil soluble succinimide dispersant additive prepared from        a functionalized hydrocarbon or polymer reacted (e.g.        derivatized) with a “heavy polyamine”. “Heavy polyamine” as        referred to herein includes higher oligomers or mixtures of        higher oligomers of polyalkylene, e.g. polyethylene, amines        containing, e.g., essentially no tetraethylenepentamine, at most        small amounts of pentaethylenehexamine, but primarily oligomers        with 6 to 12, preferably 7 to 12, nitrogens per molecule and        more branching than conventional polyamine or polyamine        mixtures; and,    -   (d) a conductivity improver comprising a hydrocarbon soluble        copolymer of an alkylvinyl monomer and a cationic vinyl monomer,        wherein the copolymer has an alkylvinyl monomer unit to cationic        vinyl monomer unit ratio of from about 1:1 to about 10:1, the        copolymer having an average molecular weight of from about 800        to about 1,000,000.

The heavy polyamine as the term is used herein contains six or more, upto about 12, nitrogens per molecule, but preferably comprisespolyalkylene polyamine oligomers containing 7 or more nitrogens permolecule and with 2 or more primary amines per molecule. The heavypolyamine comprises more than 28 wt. % (e.g. >32 wt. %) total nitrogenand an equivalent weight of primary amine groups of 120-160 grams perequivalent. Commercial dispersants are based on the reaction ofcarboxylic acid moieties with a polyamine such as tetraethylenepentamine(TEPA) with five nitrogens per molecule. Commercial TEPA is adistillation cut and contains oligomers with three and four nitrogens aswell. Other commercial polyamines known generically as PAM, contain amixture of ethylene amines where TEPA and pentaethylene hexamine (PEHA)are the major part of the polyamine, usually less than about 80%.Typical PAM is commercially available from suppliers such as the DowChemical Company under the trade name E-100 or from the Union CarbideCompany as HPA-X. This mixture typically consists of less than 1.0 wt. %low molecular weight amine, 10-15 wt. % TEPA, 40-50 wt. % PEHA and thebalance hexaethyleneheptamine (HEHA) and higher oligomers. Typically PAMhas 8.7-8.9 milliequivalents of primary amine per gram (an equivalentweight of 115 to 112 grams per equivalent of primary amine) and a totalnitrogen content of about 33-34 wt. %.

Alkylene polyamines in general, including heavy polyamines, exhibitsynergy with the olefin polysulfonic/polymeric polyamine conductivityimprover while only the heavy polyamines exhibit synergy with thecopolymeric conductivity improver.

The oil soluble dispersant additive used in the present invention isprepared by a derivatization (imidization), using an alkylene polyamine,of functionalized hydrocarbons or polymers wherein the polymer backboneshave a number average molecular weight (Mn) of greater than 300.Preferably 800 to 7500, most preferably 900 to 3000. The preferrednumber average molecular weight depends on the properties of theparticular backbone. For example, for ethylene alpha olefin copolymersthe preferred molecular weight is 1500 to 5000 (e.g. 2000-4000). Forpolybutenes the preferred molecular weight is 900 to 3000. A typicalexample of functionalized polymer is polyisobutenyl succinic anhydride(PIBSA) which is a reaction product of polyisobutene and maleicanhydride. This reaction can occur via halogen-assistedfunctionalization (e.g. chlorination), the thermal “ene” reaction, orfree radical addition using a catalyst (e.g. a peroxide). These reactionare well known in the art. In the present invention the functionalizedbackbones are subsequently derivatized with an alkylene polyamine. Inthe case of PIBSA, the reaction with the polyamine yields apolyisobutenyl succinimide.

The weight average molecular weight of the polysulfone will be in therange of 10,000 to 1,500,000 with the preferred range being 50,000 to900,000 and the most preferred molecular weight range being in the rangeof about 100,000 to 500,000. The olefins useful for the preparation ofthe polysulfones may have about 6 to 20 carbon atoms, preferably about 6to 18 carbon atoms, with 1-decene polysulfone being particularlypreferred. The preparation of these materials is known in the art asdescribed for example in U.S. Pat. No. 3,917,466. The polymericpolyamine component is prepared by heating an amine with epichlorohydrinin the molar proportions of 1:1 to 1:1.5 in the range of 50° C. to 100°C. Suitable aliphatic primary amines will have about 8 to 24 carbonatoms, preferably about 8 to 12 carbon atoms, with the aliphatic groupbeing preferably an alkyl group. If the amine used is an N-aliphatichydrocarbyl alkylene diamine, the aliphatic hydrocarbyl group will have8 to 24 carbon atoms and will preferably be alkyl and the alkylene groupwill have 2 to 6 carbon atoms. The preferred N-aliphatic hydrocarbylalkylene diamine is N-aliphatic hydrocarbyl 1,3-propylenediamine whichare commercially available. A preferred commercially available polymericpolyamine is believed to be the polymeric reaction product ofN-tallow-1,3-propylenediamine with epichlorohydrin sold as “Polyflo 130”sold by Universal Oil Co. The polymeric polyamine reaction product willhave a degree of polymerization of about 2 to 20. The description ofthese materials is also disclosed in U.S. Pat. No. 3,917,466.

Preferably, the polymeric polyamine reaction product component will beused in the form of a sulfonic acid salt. Useful are oil solublesulfonic acids such as alkane sulfonic acid or an aryl sulfonic acid.Particularly suitable is dodecyl benzene sulfonic acid or dinonylnaphthalene sulphonic acid.

The hydrocarbon soluble copolymer of an alkylvinyl monomer and acationic vinyl monomer is described in and may be made by the proceduresof U.S. Pat. No. 5,672,183, the entirety of which is incorporated byreference herein. In a preferred embodiment, the copolymer has analkylvinyl monomer unit to cationic vinyl monomer unit ratio of from 1:1to about 10:1, the copolymer having an average molecular weight of fromabout 800 to about 1,000,000. In another embodiment, the cationic vinylmonomer is a cationic quaternary ammonium vinyl monomer, and in apreferred embodiment is a cationic quaternary ammonium acrylate monomeror a cationic quaternary ammonium methacrylate monomer. In anotherembodiment, the cationic vinyl monomer corresponds to the formula:

wherein Z is selected from the group consisting of nitrogen, phosphorusand sulfur, X is a non-halogen atom, R is selected from the groupconsisting of —C(═O)O—, —C(═O)NH—, straight chain and branched alkylenegroups, divalent aromatic groups and divalent alicyclic groups, R³ isselected from the group consisting of hydrogen and methyl, R⁴ is astraight chain or branched alkylene of up to about twenty carbon atoms(C₁-C₂₀), and R⁵, R⁶ and R⁷ are independently each a straight chain orbranched alkyl of up to about twenty carbon atoms, provided however thatif Z is sulfur R⁷ is absent. Optionally, a copolymer of an alkyl vinylmonomer and a nitrile-containing monomer may be used in conjunction withthe copolymer of alkylvinyl monomer and cationic vinyl monomer.

The oil-soluble succinimide dispersants are used in the compositions ofthe present invention (on an active ingredient basis, i.e., withoutregard to carrier oil or solvent) in amounts ranging from 5-400 ppm,preferably about 10-160 ppm (by weight), such as about 10-60 ppm.

The polysulfonic-polyamine mixture conductivity improver or thealkylvinyl monomer-cationic vinyl monomer copolymer conductivityimprover may each be used in amounts from 0.10-5 ppm, preferably about0.25-1 ppm.

The compositions of this invention may also contain a phenolicantioxidant and the amount of phenolic antioxidant compound incorporatedmay vary over a range of about 1-100 ppm, preferably about 10-50 ppm,such as about 25 ppm by weight.

The preferred antioxidant phenolic compounds are the hindered phenolicswhich are those which contain a sterically hindered hydroxyl group.These include those derivatives of dihydroxy aryl compounds in which thehydroxyl groups are in the o- or p-position to each other. Typicalphenolic antioxidants include the hindered phenols substituted withalkyl groups of a total of 6 or more carbon atoms and thealkylene-coupled derivatives of these hindered phenols. Examples ofphenolic materials of this type are 2,6-di-t-butyl-4-methyl phenol (BHT,butylated hydroxy toluene); 2-t-butyl-4-heptyl phenol; 2-t-butyl-4-octylphenol; 2-t-butyl-4-octyl phenol; 2-t-butyl-4-dodecyl phenol;2,6-di-t-butyl-4-heptyl phenol; 2,6-di-t-butyl-4-dodecyl phenol;2-methyl-6-di-t-butyl-4-heptyl phenol; and2-methyl-6-di-t-butyl-4-dodecyl phenol. Examples of ortho coupledphenols include 2,2′-bis(6-t-butyl-4-heptyl phenol);2,2′-bis(6-t-butyl-4-octyl phenol); and 2,2′-bis(6-t-butyl-4-dodecylphenol). Sulfur containing phenols can also be used. The sulfur can bepresent as either aromatic or aliphatic sulfur within the phenolicantioxidant molecule. BHT is especially preferred, as are 2,6- and2,4-di-t-butylphenol and 2,4,5- and 2,4,6-triisopropylphenol, especiallyfor use in jet fuels.

The compositions will preferably contain about 0.1-50 ppm of a metaldeactivator, preferably 1-10 ppm by weight. Examples of suitable metaldeactivators include:

-   -   (a) Benzotriazoles and derivatives thereof, for example, 4- or        5-alkylbenzotriazoles (e.g. tolutriazole) and derivatives        thereof; 4,5,6,7-tetrahydrobenzotriazole and        5,5′-methylenebisbenzotriazole; Mannich bases of benzotriazole        or tolutriazole, e.g.        1-[bis(2-ethylhexyl)aminomethyl]tolutriazole and        1-[bis(2-ethylhexyl)amino-methyl]benzotriazole; and        alkoxyalkylbenzotriazoles such as        1-(nonyloxymethyl)-benzotriazole, 1-(1-butoxyethyl)benzotriazole        and 1-(1-cyclohexyloxybutyl)-tolutriazole;    -   (b) 1,2,4-triazoles and derivatives thereof, for example,        3-alkyl(or aryl)-1,2,4-triazoles, and Mannich bases of        1,2,4-triazoles, such as        1-[bis(2-ethylhexyl)aminomethyl-1,2,4-triazole;        alkoxyalkyl-1,2,4-triazoles such as        1-(1-butoxytheyl)-1,2,4-trizole; and acylated        3-amino-1,2,4-triazoles;    -   (c) Imidazole derivatives, for example,        4,4′-methylenebis(2-undecyl-5-methylimidazole) and        bis[(N-methyl)imidazol-2-yl]carbinol octyl ether;    -   (d) Sulfur-containing heterocyclic compounds, for example        2-mercaptobenzothiazole, 2,5-dimercapto-1,3,4-thiadiazole and        derivatives thereof; and        3,5-bis[di(2-ethyl-hexyl)aminomethyl]-1,3,4-thiadiazolin-2-one;        and    -   (e) Amino compounds and imino compounds, such as        N,N′-disalicylidene propylene diamine, which is preferred,        salicylaminoguanadine and salts thereof.

The fuel oil compositions of this invention may also contain one or moreother additives commonly employed in fuels and present in such amountsso as to provide their normal attendant functions. Examples are coldflow improvers such as ethylene-unsaturated ester copolymers, combpolymers containing hydrocarbyl groups pendant from a polymer backbone,polar nitrogen compounds, compounds having a cyclic ring system havingat least two substituents of the formula -A-NR¹⁵R¹⁶ where A is linear orbranched hydrocarbylene and R¹⁵ and R¹⁶ are C₉-C₄₀ hydrocarbyl,hydrocarbon polymers such as ethylene alpha-olefin copolymers,polyoxyethylene esters, ethers and ester/ether mixtures such as behenicdiesters of polyethylene glycol. Other additives include lubricityadditives such as fatty acids, dimers of fatty acids, esters of fattyacids or dimers of fatty acids, corrosion inhibitors, anti-icingadditives such as ethylene glycol monomethyl ether or diethylene glycolmonomethyl ether, biocides, thermal stability additives, anti-rustagents, anti-foam agents, demulsifiers, detergents, dispersants, cetaneimprovers, stabilisers, antioxidants, static dissipator additives andthe like.

The fuel oil may be a hydrocarbon fuel such as a petroleum-based fueloil for example gasoline, kerosene or distillate fuel oil. The fuel oilcan comprise atmospheric distillate or vacuum distillate, or cracked gasoil or a blend in any proportion of straight run and thermally and/orcatalytically cracked distillates. The most common petroleum distillatefuels are kerosene, jet fuels, diesel fuels, low sulfur diesel fuels andultra low sulfur diesel fuels, automotive gas oil, heating oils, premiumheating oils and heavy fuel oils. The heating oil or diesel fuel may bea straight atmospheric distillate, or it may contain minor amounts, e.g.up to 35 wt. %, of vacuum gas oil or cracked gas oils or of both.

Heating oils may be made of a blend of virgin distillate, e.g. gas oil,naphtha, etc and cracked distillates, e.g. catalytic cycle shock. Arepresentative specification for a diesel fuel includes a minimum flashpoint of 38° C. and a 90% distillation point between 282 and 380° C.(see ASTM Designations D-396 and D-975).

The fuel oil may have a sulfur concentration of 0.2% by weight or lessbased on the weight of the fuel. Preferably, the sulfur concentration is0.05% by weight or less, such as 0.035% by weight or less or 0.01% byweight or less. The art describes methods for reducing the sulfurconcentration of hydrocarbon middle distillate fuels, such methodsincluding solvent extraction, sulfuric acid treatment, andhydrodesulfurisation. The additive of the invention is advantageous inthe fuels having low sulfur contents, providing lubricity improvementand detergency.

Also, the fuel oil may be a biofuel, i.e. come from an animal orvegetable source, for example a vegetable or animal oil or both orderivatives thereof, or a mineral oil as described above in combinationwith biofuel.

Vegetable oils are mainly triglycerides of monocarboxylic acids, e.g.containing 10-25 carbon atoms of the structure shown below;

where R is an aliphatic radical of 10-25 carbon atoms which may besaturated or unsaturated.

Generally, such oils contain glycerides of a number of acids, the numberand kind varying with the source vegetable of the oil.

Examples of oils are rapeseed oil, tall oil, coriander oil, soyabeanoil, cottonseed oil, sunflower oil, castor oil, olive oil, peanut oil,maize oil, almond oil, palm kernel oil, coconut oil, mustard seed oil,beef tallow and fish oils. Rapeseed oil, which is a mixture of fattyacids esterified with glycerol, is preferred as it is available in largequantities and can be obtained in a simple way by pressing fromrapeseed.

Examples of derivatives thereof are alkyl esters, such as methyl esters,of fatty acids of the vegetable or animal oils. Such esters can be madeby transesterification. The preferred alkyl esters of fatty acids arethe methyl esters of oleic acid, linoleic acid, linolenic acid anderucic acid.

Commercial mixtures of the stated kind are obtained for example bycleavage and esterification of natural fats and oils by theirtransesterification with lower aliphatic alcohols. For production oflower alkyl esters of fatty acids, it is advantageous to start from fatsand oils with high iodine number, such as, for example, sunflower oil,rapeseed oil, coriander oil, castor oil, soyabean oil, cottonseed oil,peanut oil or beef tallow. Lower alkyl esters of fatty acids based on anew variety of rapeseed oil, the fatty acid component of which isderived to more than 80 wt. % from unsaturated fatty acids with 18carbon atoms, are preferred.

The invention is particularly useful for the formulation of turbinecombustion fuel oils (jet fuels) which are generally those hydrocarbonfuels having boiling ranges within the limits of about 150° to 600° F.(65 to 315° C.) and are designated by such terms as JP-4, JP-5, JP-7,JP-8, Jet A, Jet A-1. JP-4 and JP-5 are fuels defined by U.S. militaryspecification MIL-T-5624-N and JP-8 is defined by U.S. MilitarySpecification MIL-T83133-D. Jet A, Jet A-1 and Jet B are defined by ASTMspecification D1655.

The invention will now be described by way of example only.

EXAMPLES

The three fuels described below were tested.

Fuel Details: Base Fuel 2 Base Fuel 3 Base Fuel 4 Test Units ResultResult Result Density @ 15° C. Kg/L 814 829 835 Distillation IBP ° C.168 174.6 216.6 10% 184.2 228.9 240.7 50% 210.2 274.0 277.0 90% 235.2322.7 327.6 FBP 255 349.2 358.1 RESIDUE vol % 1.1 2.0 2.0 LOSS vol % 1 00 FIA Analysis vol % Aromatics 15.2 28.2 Total Sulfur IP % m/m 0.0006<0.001 0.0036 336/95 Flash Point (Abel) 54 IP 170/99 Freezing point −54IP 16/98 Viscosity at −20° C. 5.48 IP 71 Existent gum <1 CP −20 CFPP −9−19

Code Description of Additive Dispersant A a succinimide made from apolyisobutenyl (Mn 950) succinic anhydride reacted with a heavypolyamine having a 10-12% pentaethylene hexamine content, 32% nitrogenand 7.7 meq/g of primary nitrogen, the succinimide having 3.85%nitrogen. Dispersant B a succinimide made from a polyisobutenyl (Mn1000) succinic anhydride and the same heavy polyamine used to makeDispersant A, the succinimide having 4.74% nitrogen. Dispersant C asuccinimide made from a polyisobutenyl (Mn 950) succinic anhydridereacted with a commercial PAM mixture of ethylene polyamines, thesuccinimide having 2.0% nitrogen. Dispersant D a succinimide made from apolyisobutenyl (Mn 1000) succinic anhydride reacted with tetraethylenepentamine the succinimide having 1.35% nitrogen Dispersant E asuccinimide made from a polyisobutenyl (Mn 2250) succinic anhydridereacted with pentaethylene hexamine the succinimide having 0.7% nitrogenStadis 450 66% toluene, 13.3% 1-decene polysulfone, 13.3% polyamine (areaction product of N-tallow-1,3- propylenediamine and epichlorohydrin)and 7.4% dodecylbenzene sulfonic acid. T3514 a commercial hydrocarbonsoluble copolymer of an alkylvinyl monomer and a cationic vinyl monomersold as “T3514” by Baker Petrolite as a conductivity improver.

Fuel Conductivity Tests

The fuels described above were tested for conductivity using an EMCEE1152 conductivity meter. The results are given in Table 1 below. Testswere carried out on the fuel without any additives, fuels 2, 3 and 4containing each of Dispersant A and B (which were dispersants made withheavy polyamines), Stadis 450 and T3514, the latter two being commercialconductivity additives. Fuels containing a combination of this inventionexhibit a synergistic cooperative effect in low conductivity fuels notpredictable from the values obtained when the additives are testedindividually. “BF” refers to Base Fuel. Dispersants C, D and E (madewith conventional ethylene polyamines, i.e., not the heavy type) weretested only in fuel 2 and showed synergy with the “Stadis 450”commercial conductivity improver. Dispersants made from the heavypolyamines show synergy with both types of commercial conductivityimprovers. Conductivity Conductivity Conductivity (pS/m) (pS/m) (pS/m)Additive ppm BF3 BF4 BF2 Base Fuel 0 18 1.7 3 Stadis 450 0.25 39.7 38.755 T3514 0.25 46.7 9.7 58 Dispersant A 33 65 34.7 523 Dispersant A +33 + 0.25 96.7 131.3 707 Stadis 450 Predicted 104.7 73.4 578 DispersantA + Stadis 450 Dispersant A + 33 + 0.25 93.7 78 617 T3514 Predicted111.7 44.4 581 Dispersant A + T3514 Dispersant B 40 150 106.3 825Dispersant B + 40 + 0.25 189.7 202.3 954 Stadis 450 Predicted 189.7 145880 Dispersant B + Stadis 450 Dispersant B + 40 + 0.25 195.3 153.3 923T3514 Predicted 196.7 116 883 Dispersant B + T3514 Dispersant C 25 188Dispersant C + 25 + 0.25 317 Stadis 450 Predicted 243 Dispersant C +Stadis 450 Dispersant D 19 100 Dispersant D + 19 + 0.25 240 Stadis 450Predicted 155 Dispersant D + Stadis 450 Dispersant E 29 35 DispersantE + 29 + 0.25 147 Stadis 450 Predicted 90 Dispersant E + Stadis 450

1. An improved fuel oil composition, the composition comprising a fueloil having an inherent conductivity of less than 15 pS/m and a twocomponent additive system; wherein the two component additive systemcomprises the combination of: (a) an oil soluble succinimide dispersantcomprising a functionalized hydrocarbon reacted with an alkylenepolyamine; and (b) a conductivity improver comprising (i) an olefinpolysulfone and (ii) a polymeric polyamine reaction product ofepichlorohydrin and an aliphatic primary monoamine or an N-aliphatichydrocarbyl alkylene diamine, or the sulfonic acid salt of the polymericpolyamine reaction product, or the combination of: (c) an oil solublesuccinimide dispersant comprising a functionalized hydrocarbon reactedwith a heavy polyamine, and (d) a conductivity improver comprising ahydrocarbon soluble copolymer of an alkylvinyl monomer and a cationicvinyl monomer, wherein the copolymer has an alkylvinyl monomer unit tocationic vinyl monomer unit ratio of from about 1:1 to about 10:1, thecopolymer having an average molecular weight of from about 800 to about1,000,000.
 2. A composition according to claim 1, wherein the dispersantis a polyisobutenyl succinimide.
 3. A composition according to claim 1which comprises an antioxidant.
 4. A composition according to claim 1which comprises a metal deactivator.
 5. A composition according to claim1, in which the polyisobutenyl has a molecular weight of 900-3000.
 6. Acomposition according to claim 1 which also comprises one or moreadditives selected from the group consisting of cold flow improvers,lubricity additives, corrosion inhibitors, anti-icing additives,biocides, thermal stability additives, anti-foam agents, anti-rustagents, demulsifiers, detergents, dispersants, stabilisers, staticdissipator additives and cetane improvers.
 7. A composition according toclaim 1, in which the fuel oil is a turbine combustion fuel oil.
 8. Acomposition according to claim 1, in which the fuel oil is a diesel fuelor a heating oil.
 9. A conductivity improving additive comprising thecombination of: (a) an oil soluble succinimide dispersant comprising afunctionalized hydrocarbon reacted with an alkylene polyamine; and (b) aconductivity improver comprising (i) an olefin polysulfone and (ii) apolymeric polyamine reaction product of epichlorohydrin and an aliphaticprimary monoamine or an N-aliphatic hydrocarbyl alkylene diamine, or thesulfonic acid salt of the polymeric polyamine reaction product, or thecombination of: (c) an oil soluble succinimide dispersant comprising afunctionalized hydrocarbon reacted with a heavy polyamine, and (d) aconductivity improver comprising a hydrocarbon soluble copolymer of analkylvinyl monomer and a cationic vinyl monomer, wherein the copolymerhas an alkylvinyl monomer unit to cationic vinyl monomer unit ratio offrom about 1:1 to about 10:1, the copolymer having an average molecularweight of from about 800 to about 1,000,000.
 10. The use of an additiveaccording to claim 9 to improve the conductivity of a fuel oil.